Abstract Objectives The Radboudumc Amalia Children's hospital in the Netherlands has a programme for renal transplantation in children aged ≤4 years. Children receive chronic corticosteroid sparing immunosuppressive therapy that consists of tacrolimus and mycophenolate mofetil. This work aimed to describe the PK of tacrolimus in children ≤4 years with renal transplants. Methods Paediatric renal transplant patients aged ≤4 years were included in this analysis. A PK curve of tacrolimus recorded ≤3 weeks after transplantation has been standard of care in our institution and aided in adjusting the dose in each patient to attain a target AUC0–12h of 210 μg h/l early after transplantation. Key findings Eight patients were included. The first two patients received an initial twice-daily regimen and the subsequent six patients a three-times daily regimen. Median dose-corrected AUCtau was 63 μg h/l. AUC target attainment was 37.5%. Of the remaining patients, two had an AUC very close to (around 10% below) the target. Conclusions Large interindividual variability of tacrolimus was observed and showed suboptimal AUC target attainment. In this population, an even more aggressive approach of higher doses (e.g. 0.4 mg/kg per day) and more early AUC determination should be considered. This should be evaluated prospectively in a larger group of patients.